Automatic switching system comprising direct and mutual-aid routes between selection units



July 8, 1969 P. M. LUCAS ET AL 3,454,723

AUTOMATIC SWITCHING SYSTEM COMPRISING DIRECT AND MUTUAL-AID ROUTES BETWEEN SELECTION UNITS Sheet Filed June 28, 1965 =5 E umW/on kafim V. @En nm mEww @Ea aw 53 .w m I W T m T. v 8? WM M $35 Q .m 0 W n I W N. T W 5L H U AL a L! 6%; MM w m W x w Q-Q-Qu m M HE P v AUTOMATIC SWITCHING SYSTEM COMPRISING DIRECT AND MUTUAL-AID ROUTES BETWEEN SELECTION UNITS Filed June 28,1965 Sheet 13 of v i 2 x= x x a: I J" 1 I l g 1: 1: 1: Z B l 1 I M g N 1 l l I .m 1 u: l LL i ii a l i: I g 4 FD I m 2: K l g i 1 Z- l a o x x V Q I it// i \NVENTORSI RH. LUCAS, J.r. puouesnz, :2 LE army M. M. ROOZIEQ ATTORNEY aajwg 3,454,723 AUTOMATIC swrrcnme SYSTEM COMPRISING DIRECT AND MUTUAL-AID 8, 1969 P. M. LUCAS ET AL ROUTES BETWEEN SELECTION UNITS Sheet Filed June 28, 1965 mamas:

EN. LUCAS, J-F. DUOUESHE, P. LE. GAP-Li HM. ROUZIEQ m mc ATT RNEY: a-z-ffllg Jul 8, 1969 P. M. LUCAS ET AL AUTOMATIC SWITCHING SYSTEM COMPRISING DIRECT AND MUTUAL-AID ROUTES BETWEEN SELECTION UNITS Sheet 4 Filed June 28, 1965 Jlfly 8, 1969 P. LUCAS 'ETAL 3,454,723

AUTOMATIC SWITCHING SYSTEM COMPRISING DIRECT AND MUTUAL-AID ROUTES BETWEEN SELECTION UNITS Filed June 28, 1965 Sheet 5 of 7 7 i I I0 :ryc I Swz'lc/u'a Line I Ale/work E qulPme/Ir DIRECT JELEL'T/O/V LIII L i wzgfik 2 I Marking 1 I circui/s of Me I Image nefwark F I d I 1 9 22% l ZQ I 2551 r Y 'T HM I Decoder I I I J I I 2 Add/ea") 2 I 153 105 I I Programmer I I I I I I 25/ I I I I I Dis/ribulw 2 I I I06 I I I I -/07 I I Del/90mg indicator J I I I I I 1 I .Sfore [or pending calls I 52 I [0 4 I 1 (and incoming Ibdicafor) ;I Q I Transmission I I I Logic par/inn of [he I I line ulcer/on unil' .L 350 Access /0 .sfores INVENTOIZ5= m1. LUCAS, J.E DUQUESM, P. LE eau. HJIROUZIEQ "women July 8, 1969 LUCAS ETAL 3,454,723

AUTOMATIC SWITCHING SYSTEM COMPRISING DIRECT AND MUTUAL-AID ROUTES BETWEEN SELECTION UNITS Filed June 28, 1965 Sheet 6 of 7 Jumbo I 5 iver/r 0/ I779 U A a a a n sfore of Me suzuni! (D) 56' EF I ar/r share 7 ansfer CIICUIIS fol/1e sfores I J{, i [F lAac DEF Kl. N I

4/0 Pou/e se/echbn reg/Sher Program mar 109/1: Porh'on of Me yroup selecflbn uni! Access fa fhe 618,11

(a mpufers INVENTOR$= EH. was, 4;. puouasnE, P. LE elm. vr'm ROUZIEQ TOQNE Y:

July 8-, 1969 P. M. LUCAS ETAL 3,454,723- AUTOMATIC SWITCHING SYSTEM COMPRISING DIRECT AND MUTUAL-AID ROUTES BETWEEN SELECTION UNITS Filed June 28, 1965 Sheet 7 of 7 PM. LUCAS, J.F- OUOUESHE, P LE GALLr' HM. QOUZIER ATTORNEY:

United States Patent Ofice 3,454,723 Patented July 8, 1969 3,454,723 AUTOMATIC SWITCHING SYSTEM COMPRISING DIRECT AND MUTUAL-AID ROUTES BETWEEN SELECTION UNITS Pierre M. Lucas, 20 Rue Tariel, Issy-les-Monlineaux, France; Jean F. Duquesne, 41 Rue Esquirol, Paris, France; Pierre Le Gall, 4 Parc de la Berengere, Saint Cloud, France, and Michel M. Rouzier, 15 Chamin de la Sabliere, Vauhallan, France Filed June 28, 1965, Ser. No. 467,592 Claims priority, application France, June 30, 1964, 980,179 Int. Cl. H04m 3/00 U.S. Cl. 179-18 5 Claims ABSTRACT OF THE DISCLOSURE A switching arrangement for an automatic telecommunication exchange comprising line selection units connected to subscribers lines, group selection units connected to junction circuits and direct links connecting the line and group selection units. Mutual-aid links are provided between outputs (line selection unit side) of certain group selection units and inputs (junction circuit side) of other group selection units, the path between a subscribers line and a junction circuit thus including two cascade-connected group selection units.

The line selection units include several line selection switches and line selection partial links connecting the same therebetween and similarly the group selection units have several group selection switches and group selection partial links connecting the same therebetween. A routing network is associated to the switching network and also comprises line selection partial links, group selection partial links, direct links and mutual-aid links. A selector means searches in a first choice search routing paths including a line selection partial link, a direct link and a group selection partial link and in a second choice search routing paths including a line selection link, a direct link, a mutual-aid link and a group selection partial link. Means are provided for marking the switching network links corresponding to the routing network links forming a path found available.

The present invention relates to automatic telephone switches having a switching network of the high capacity spatial type with centralized control of the route selection.

U.S. Patent No. 3,274,343 issued Sept. 20, 1966 in the names of the first two of the present applicants describes an electro-mechanical switching network with electronic control, comprising subscriber selection units and group selection units of which the first, which constitute remote satellites, are connected to the second which constitute a telephone exchange, by three wire connection lines and by route selection lines which may be marked by continuous potentials in such a manner that the only information which it is necessary to exchange between the satellite and the exchange are the numbers of the calling subscriber and called subscriber and that which indicates to the exchange that the selection or the connection of a called subscriber or calling subscriber is in course or terminated in the satellite. The switches forming the subscriber selection units and the switches forming the group selection units are crossbar switches formed by two switch frames, each of the horizontals of one of these switches in the first frame being connected to a vertical in the switch of the same rank in the second frame by link wires inside the stage. The route selection lines comprise a preselection route wire and a final route wire passing through make contacts of relays designating the calling subscriber or called subscriber to be connected in the subscriber selection unit and respectively through relay rest contacts of a vertical, the action of which is necessary either to connect said calling subscriber to a local connection or junction circuit or to connect said called subscriber to a link between subscriber selection units and group selection units. In this network, the group selection units only comprise two switch stages as subscriber selection units, and if a direct final route cannot be established between a connecting circuit and a subscriber through the group selection stage and the sub scriber selection stage which correspond in cascade the cofinection cannot be eifected. It follows that in order to avoid partial blockage of the network it is necessary to use, in the group selection units, high capacity switches which are often not fully utilised.

In order to overcome this disadvantage recourse has been had to special overflow units through which the traffic is caused to pass which has not been able to reach the line selection units directly. This method has the disadvantage of necessitating a considerable increase in the number of crosspoints.

Another process used for the same object consists in having recourse to mutual aid between group selection units, which consists in connecting a group selection unit and a line selection unit between which there is no direct link available, by means of another group selection unit, but it has not been possible to extend this process to selection units comprising more than one or two principal switch stages because of diificulties involved as a result of the excessive number of possible routes to be tested. Furthermore, statistical studies show that on the one hand the process of general mutual aid associated with two switch stages is only suitable for exchanges with at most 15,000 subscribers, otherwise too many crosspoints are lost by using excessively large switches, and on the other hand for exchanges having more than 10,000 subscribers it is an advantage to associate three main stages with the general mutual aid procedure.

The main object of the present invention is to achieve an optimum use of the connection points of a switch network of the high capacity spatial type.

A particular object of the invention is to enable the process of general mutual aid to be associated with three main stages of switches.

According to the invention, an automatic telephone switch having a switching network of the high capacity spatial type and with centralised control of the route selection comprises line selection units serving the subscribers lines, group selection units having three stages of switches connected on the one hand to junctions, on the other hand to said line selection units through direct links and also between themselves by mutual aid links, electronic means permitting the selection of direct routes for several connections to be efiected simultaneously, according to the principle of conditional selection extended to all stages of the network, and, in the case of failure of a direct selection, permitting the selection of a mutual-aid route in all the available group selection units, means for marking and for connecting the selected routes, and means for limiting the resulting unavailability solely to those routes which are affected by the marking and connection process.

Since this process of marking and connection only contributes to a small extent to the fictitious busying of the network, it may be effected by slow means, for example by means of crossbar switches or of reed relays.

The route selection in the group selection unit is preceded by a reservation of the line selection unit and by a marking of the links which can be used in this latter unit to reach the given line. This marking may be relatively slow because it has no influence on the duration of the actual selection.

The selection of a mutual-aid route is effected under the control of a mutual-aid route selector which co-ordinates the selection operations between the various group selection units available and in particular solves the problem of competition between the various group selection units each of which is seeking a route towards the same line selection unit through a multiplexing in time of the test moments for the various links tried. After a mutual aid route leading to the desired line selection unit has been found in a group selection unit, the search is interrupted in the other engaged groups and a route adapted to extend the mutual aid route found is sought in the original group selection unit.

The reliability of operation of the whole is assured in particular by the plurality of group selection units each of which can carry on its route selection independently and by the subdivision of the common members, the purpose of which is to co-ordinate the relations and the exchanges of information between the group selection units and the line selection units.

The invention will be better understood by reading the following description and examining the accompanying drawings, in which:

FIGURE 1 is a block diagram of the switching network according to the invention;

FIGURE 2 is a basic diagram of the image circuit associated with the switching network of FIGURE 1 to permit the selection of routes;

FIGURES 3a, 3b are basic diagrams of the selection of direct routes and mutual aid routes respectively'in the circuit of FIGURE 1;

FIGURES 4a, 4b, 4c are block diagrams of the logic control circuits ensuring the operation of the circuit in FIGURE 1.

FIGURE 1 illustrates diagrammatically the switching network formed of rectangular matrices of crosspoints such as the switches of the crossbar type or switches of the reed relay type. v

In this diagram the switches are arranged in switching stages and in selection units. A switching stage is the assembly of all the switches which have the same rank over the various routes of the network starting, for example, from the subscribers line and travelling towards the junctions. FIGURE 1 shows a five-stage network of which the first two form the line selection units, and the other three the group selection units. A line selection unit consists of a combination of switches in the first two stages which are interconnected, that is to say inside each line selection unit, each switch in the stage 1 is connected through a link to each switch in the stage 2. A group selection unit consists of an assembly of switches belonging to the stages 3, 4 and 5 and which are interconnected in pairs as in the figure. A group selection unit consists of the interconnection of selection sub-units. Although the grading of a group selection unit is completely symmetrical, it is convenient for the explanation to consider on the one hand switches in the stages 3 and 4 and on the other hand those in stage 5.

A combination of switches in the group selection unit which belong to the stages 3 and 4, and which are interconnected in pairs will be called a grading sub-unit. A combination of switches in stage '5 belonging to the group selection unit and connected to the outputs of the same rank in all the switches in stage 4 will be called a group sub-unit.

By way of clarification and at the same time to specify the grading plan selected by way of example, the fundamental parameters permitting a route to be designated :ompletely in a group selection unit G, will be designated by the letters A to F to which any values may be given. In the same manner the fundamental parameters which enable a route to be designated completely in a line selection unit N will be designated by the letters H to L.

In order to facilitate understanding of the grading plan, these parameters, with numerical indices representing the various values which they may assume, are used to designate the following assemblies- G: group selection unit N: line selection unit DG: grading sub-unit in the group selection unit G BG: group sub-unit in the group selection unit G BC: switch in stage 5 in a group sub-unit BG CD: switch in stage 4 in a grading sub-unit 'DG DE: switch in stage 3 in a grading sub-unit DG J N: switch in stage 2 in a line selection unit N KN: switch in stage 1 in a line selection unit N By agreeing to designate the rank of an input or of an output of a switch by the same parameter as the rank of the switch in the adjacent stage in which this input or this output give access, it will be seen that the link, in the group selection unit for example, connecting the switch designated by BC to the switch designated by CD may be characterised by BCD. This means that the condition necessary for two switches in adjacent stages to be effectively connected by a link is that the characteristic parameter which they have in common, C in this example, has the same numerical value in both.

The successive links constituting the route inside a group selection unit G will therefore be designated respectively by ABCG, BCDG, CDEG, DEFG, the letter G being assigned to the group selection unit.

Similarly in a line selection unit N they will be designated by HJN, JKN, KLN, the letter N being assigned to the line selection unit.

The data of the parameter G and of the parameters ABCDEF on the one hand, of the parameter N and of the parameters HJKL on the other hand, permit a complete definition of two associated half-routes connecting a junction designated by ABCG to an output of the group selection unit G designated by DEFG on the one hand and an input of the line selection unit N designated by HJN to a su'bscribers line belonging to this same unit N and designated by KLN on the other hand. These two half-routes will constitute a physical connection between the junction ABCG (belonging to the group selection unit G) and the subscribers line KLN (belonging to the line selection unit N) if the parameters DEFG and HJN designate the same link considered as an output from G and as an input of N.

Some of the outputs DEFG from a group selection unit G are connected to inputs HJN of the various line selection units N and in accordance with the principle of mutual aid between group selection units, others of the outputs (DEFG) in each unit G are connected to inputs AB'C'G connected to the various other group selection units G. The rule for distribution between the former, known as direct selection links, and the second known as mutual-aid links as well as the rules for connection between on the one hand direct links between the various group selection units and the various line selection units, and on the other hand the mutual-aid links between the outputs and the inputs of the various group selection units are selected in such a manner as to satisfy the following requirements:

(a) To simplify the fitting of the information registers to prepare the route tests;

'(b) Through a grouping of the addresses of the links, to enable the availability test to be easily limited to the only links which are strictly useful;

(c) To facilitate the extension of the network from a small capacity to its full capacity.

The selection of a route enabling a junction to be connected to a subscribers line, characterised respectively ABCG and KLN comprises one or two phases according to whether a direct link (designated by DEPG and H] N), can or cannot be borrowed between the selection units G and N. If the selection of a direct link fails as a result of congestion, recourse is had to the mutualaid. For this a route is first sought between the given subscribers line KLN and a mutual-aid link A'B'C'G' which is capable of connecting to the given selection unit G, any other selection unit G other than G, this secondary route selection being of the same nature as the direct route selection except that it involves the .inputs ABCG' which are mutual-aid links and not the junctions ABCG, and on the other hand it takes place in all the group selection units G other than G which are available at this moment. When this secondary route selection has led to the selection of a mutual-aid link ABCG' and to the route capable of connectin it to the subscribers line KLN, it remains to select a mutual aid route, that is to say to select a free path (in the input ABCG and the mutual-aid link (DEFG), which there is connected the given junction) between this given input ABCG and the mutual-aid link (DEPG) --which corresponds to the input A'B'CG' selected at the" moment. If such a mutual-aid route selection is successful, the complete route comprises three portions, namely:

In the selection unit G, a path between the junction ABCG and the mutual-aid link (DEFG) (output from G).

In the selection unit G, a path between this same mutual-aid link, here designated 'by A B'CG (as an input of G), and a direct selection link D'E'FG (output from G).

In the line selection unit N, a path between this same direct selection link, here designated by (HJN) (as an input of N), and the given subscribers line KLN.

If the secondary route selection has been successful but the mutual-aid route selection is not successful, as a result of an internal blockage in the group selection unit G, the secondary route selection is resumed in such a manner as to find another mutual-aid link ABCG', if there is such a one, and a fresh attempt is made to' effect a mutual aid selection relating to this link. Through a methodical exploration of all the possibilities, an example of one of which will be given later on, it is thus possible to effect the selection of a route very rapidly, by using or not using mutual aid through the whole network. Since all the possible routes are thus tested before a connection is made (the direct routes as a first choice and the routes with mutual aid as a second choice). it may be said that the choice of route is effected with conditional selection through the whole of the network, that is to say in the example of FIGURE 1 through five or eight stages of switches according to whether the direct route is taken or not.

By way of example if the parameters A to F and H are given ten possible values from 0 to 9, the parameters G and I eight possible values from 0 to 7, the parameter K twenty possible values from 0 to 19, the parameter L twenty-five possible values and moreover, if it is specified that of the 100 links EF leaving a sub-element D of a selection unit G, 60 are connected to the line selection units N and 40 are mutual-aid links, the network thus constituted will comprise altogether:

Eight group selection units G to G each having 1,000 inputs of which 600 are junctions ABCG and 400 are mutual-aid inputs AB'CG' and 1,000 outputs of Such a switching network comprises approximately 580,000 crosspoints of which 240,000 are in the 8 group selection units and 336,000 in the 60 line selection units, and it is capable of a traffic flow of 3,000 Erlangs. It is recalled that the Erlang is the telephone traffic unit corresponding to an average of one call present on a trafiic carrying facility.

The switches of which the network is composed have dimensions of 10 x 10 in the group selection units and dimension of 10 x 20 and 8 x 25 in the line selection units that is to say 10 x 20 for the switches IN in the stage 2 and 8 x 25 for the switches KN in stage 1.

It should be understood these figures are only given by way of example for a network of large dimensions comprising three stages of switches in the group selection units, with mutual-aid links connecting these units in pairs in accordance with the object of the invention. In order to simplify the explanation, it has been assumed that there is only one connecting link between two switches belonging to two adjacent switching stages but it is obvious that these restrictions may easily be lifted provided that the method of allocating the fundamental parameters and of specifying the selected interconnection rules are modified appropriately.

GENERAL PRINCIPLES OF THE SELECTION OF ROUTES It will now be explained, with reference to FIGURE 2 and FIGURES 3a and 3b how, in a circuit defined by the fundamental parameters specified above, it is possible to determine whether a route consisting of a series of connectable links, that is to say such that there is a crosspoint capable of connecting each pair of adjacent links, is or is not available to establish a connection.

Since two switches belonging to adjacent stages such as BC and CD are connected by a link if the common parameter such as C assumes the same value in both, it is sufficient, in order to define a connectable route, to give numerical values to the groups of parameters:

ABCDEFG which designates the portion of a route connecting a junction ABCG to a direct selection link DEFG in the unit G and H-JKLN which designates the portion of a route connecting a direct selection link H] N to a subscribers line KLN in the unit N with the additional condition that DEFG and H] N designate the same direct selection link.

Since ABCG and KLN have prescribed values representing respectively the junction and the given subscribers line it will be seen that the selection of a direct route means fixing numerical values for the remaining parameters DEFHJ while satisfying the following conditions:

(1) DEFG and H] N are always the two designations for one and the same link.

(2) This link as well as all the other links composing the route namely.BCD, CDE, in the group selection unit G and J K in the line selection unit N are available that is to say they have not already been used as components of a route established in the network.

(3) By hypothesis, the end lines ABCG and KLN are assumed to be not busied in an existing connection, this fact having it necessary been verified before undertaking the selection of a route.

The second of these conditions comes to the same thing as checking that the condition of availability is verified on the four intermediate links BCD, CDE, DEF and J K. For this purpose, with each of these links, there is associated an element having a binary characteristic, for example, a relay contact or a transistor gate, having the property of being conducting if the corresponding link is available, and the second condition above is obtained only in the case where a circuit arranged in such a manner as to comprise these four binary elements in series is r conducting. Such a circuit in which the conducting state indicates the availability of the route using the links with which are associated its elements having a binary characteristic will be designated hereinafter by the name of image-circuit.

FIGURE 2 is a basic diagram of the image-circuit of a connection network in accordance with the diagram shown in FIGURE 1. In FIGURE 2 this image-network is represented as being composed of relay contacts (a make contact being designated by a cross, a break contact by a dash perpendicular to the wire) both for the marking elements (make contacts) and for the link-availability elements (break contacts). This representation is used as an aid to understanding the principle of the image-circuit but it should be understood that the elements which constitute it generally consist of electronic gates rather than of metal contacts.

The image-circuit consists of three parts, the first 6 in the origin group selection unit G, the second 2 in the line selection unit N and the third 6' in another group selection unit G.

This latter portion which relates to the mutual-aid route selection will be studied subsequently.

DIRECT ROUTE SELECTION The first and the second portion of the image-network are associated with a direct route between a junction ABCG and a subscribers line KLN. These two portions, of which the first is only illustrated with regard to the fraction relating to a grading subunit D, lead respectively to the inputs of a plurality of gates such as 4 (DEF) each of which is associated with a direct connection link designated by DEF in the group selection unit G and by H] in the line selection unit N and they enable the state of occupation and the accessibility of these various links to be known for the proposed route selection.

The principle of the image-network for a direct route selection consists in establishing, on the one hand in all the grading sub-units D in the unit G and on the other hand in the line selection unit N, a plurality of associated connections between a marking potential and an input to the test gates such as 4 (DEF) in such a manner that only certain of these gates which characterize the routes which can be used for the connection are marked at their first and second inputs. In these circumstances, a test pulse applied to a third individual input in the test gate will be transmitted through said gate to the common test circuit which will be defined hereinafter.

In order that only those test gates which correspond to the direct links DEF which may be used to establish the connection between the given junction and subscribers line ABCG and KLN may be etfectively marked, it is necessary to set up a connection between the switches and links of the switching network on the one hand and the image-links and the gate elements inserted therethrough.

In the image network, a common point between image links corresponds to a switch of the switching network, an image-link corresponds to a link of the switching network and a closed or open gate elements corresponds to the availability or unavailability of the link of the switching network. It will be seen, for example, that by marking a single value of B in the group selection unit G, a point (BD) is selected in each sub-unit D hence the corresponding fraction of the image links (BCD). Moreover by marking a single value of C, a single intersection (CD) is selected in each sub-unit D and, in consequence, the only possible path left is through a single one of the image links (BCD). Actually it is quite clear from FIG- URE 1 that starting from a given junction ABCG there is only a single link BCD to be tested towards each subunit D. This latter is selected by the test. The values of the parameters E and F are imposed by the laws for connecting the direct links between the various group selection units and the various line selection units but, since this restriction results from the selection of the addresses by the programmer, the image circuit has no marking corresponding to this parameter and, at the output from the intersection (CD) it is possible to reach all the intersections (DE) through all the image links (CDE) and hence all the test gates (DEF) corresponding thereto. Of course, each test gate will only be effectively reached if the two availability elements of the image links (BCD) and (CDE) which are passed through in series are conducting simultaneously, which corresponds to the verification of the second of the conditions indicated above.

symmetrically, in the line selection unit N, a single one of the intersections (K) is selected by marking a value of the parameter K and in consequence the image network is restricted to the image links (JK) which are accessible, but no marking is effected corresponding to the parameter H and it is possible to reach the second inputs of the test gates through the image links (JK) which have been selected and all the image links (HI) which are available. Actually FIGURE 1 shows that in the line selection unit N, for a given subscribers line KLN, the switch K is exactly determined, but that all the input links H] into the line selection unit are accessible to the subscriber, to the extent to which they are idle and correspond to a free link JK.

In the example illustrated where it is assumed that break contacts of relays would be used to define the availability state of the links which can be used, since these elements are by nature bidirectional, it is important in .order to avoid return paths in the image circuit, to render the various image links unidirectional by means of diodes. Without this precaution it would in fact not be possible to ensure that the test gates were not marked wrongly, because stray paths might exist which would seize in the reverse direction all the available image links marked and disturb the image network.

Thus after the marking of the imposed parameters B and C has been effected in the image element G and the marking of the prescribed parameter K has been effected in the image element N, this image network therefore allows all the test gates which are accessible to the junction ABCG to be marked by their first input (wire q) and all the test gates which are accessible to the subscribers line KLN to be marked by their second input (wire 1)- The test route should be limited to the gates 4 corresponding to direct links connecting the group selection unit G which is prescribed, i.e. that to which is connected the selected connection circuit, to the prescribed line selection unit N, i.e. that to which is connected the calling or called subscriber, and of these latter only those Which are accessible both from the junction and from the subscribers line are of interest in the establishment of a route. These test gates which are of interest are recognised by the fact that they are simultaneously marked at their two inputs (wire q and wire 1) through the image network and consequently are conducting for the test pulse applied to their individual input.

After the operation of marking the image network the problem of the route test is limited to the selection of one of the test gates thus released, which is obtained by means of a sequential test, restricted by the programmer solely to those gates which are accessible both to the junction and to the subscribers line which have been designated.

SELECTION OF THE MUTUAL AID ROUTES A route established with mutual-aid through a group selection unit G consists of a mutual-aid route directed towards the unit G' through the origin selection unit G and a secondary route established through the mutual-aid unit G and the prescribed line selection unit N. This latter route is only distinguished from a direct route in that its point of origin instead of being at the junction ABCG which is clearly determined consists of a mutualaid link AB'CG which is not fixed a priori but belongs to the mutual-aid group between the units G and G.

As already indicated, the terminal selection units G and N are imposed by the selection of the junction ABCG and of the subscribers line KLN to be connected but the mutual-aid unit G is not defined a priori, the selection of a secondary route being started simultaneously, after failure of the selection of a direct route, in all the selection units G which are not occupied at this moment.

In each of the group selection elements G used for a mutual-aid, a marking of the image network is effected in such a manner as to mark, at their first input, the test gates (D'EF) of the image links D'EF which are accessible from the mutual-aid links ABCG through the group selection unit G itself. This marking uses the same first and second portions of the image network illustrated in FIGURE 2 as in the case of the direct selection previously described, but the parameters BCD which are substituted for the parameters BCD are not imposed in the same manner. In the case of the direct selection, B and C are imposed according to the number of the junction ABCG and D is indeterminate. In the case of the secondary selection B and D are indeterminate, and only half of the values of C are permitted according to the number of origin group selection unit G, and in accordance with the rule adopted for the connection of the mutual-aid links between group selection units.

In consequence the marking effected in the image network of the unit G for the secondary selection is similar to that for the direct selection except that all the values of B and half the values of C are marked instead of only one, and that in consequence it may happen that a greater number of test gates are marked at their first input.

In reality the marking of the group selection unit G effected in the image network takes place in two stages. The first stage, corresponding to the marking which has just been indicated (possible values of B and C supplied simultaneously) makes it possible to recognise whether or not there exist secondary links permitting the group selection unit G in consideration to be connected to the imposed line selection unit N.

If the existence of such a link is recognised, a second marking stage, permitting a suitable value to be selected for the parameters B and C, takes place at the same time as the mutual-aid selection in the origin unit G as will be explained hereinafter. In the course of this second stage, the various possible values of the parameters BC are successively marked in the unit G while at the same time in the origin selection unit G, the values of the parameters D and E are marked which are homologous thereto.

In the origin group selection unit G the selection of a mutual-aid link in the direction of unit G recognised as having access to the imposed line selection unit N, presupposes the marking in the image network of the test gates relating to the mutual-aid links between G and G.

The fraction of the image network affected by this marking corresponds in FIGURE 2 to the first portion 6 associated with the group selection unit G and to the third portion 6' associated with the group selection unit G.

In order to effect the selection of a mutual-aid link DEF, the two selection units G and G work together and in synchronism effect the marking of the equal parameters D and B, E and C.

In the unit G, the marking of the image network is therefore effected for a given value of B and a given value of C (fixed by the number of the junction ABCG) and successively for the various values of D.

In the unit G, the marking is effected successively for the various permitted values of B and C.

Since these markings are effected in synchronism in G and G, it follows that at a given moment, corresponding to any common value of the parameters D, E on the one hand, B, C on the other hand, the test gates (DEF) which are accessible to the junction ABCG and relative to the grading sub-unit D, are marked by their first input, and the test gates of the mutual-aid links which end in the unit G at the selection sub-unit B homologous with D are likewise marked at their second input. Thus at the same moment, in the image network of the unit G the gates D'EF corresponding to direct links accessible to the mutual aid links AB'CG connected to the switch BC of the same selection sub-unit B are marked by their first input and, in the image network of the line selection unit N, the gates (DEF/ HJN) which are accessible to the subscribers line KLN are marked by their second input.

It will then be understood, that for this value of BC and DE which have provisionally been marked, it is possible, by means of individual tests of the gates (DEF) and (DEF) controlled by the programmer for the system of route tests, to determine first of all whether there is a secondary link DEF'G which can be used, and then to select a mutual-aid link DEFG/A'BCG', the test being restricted by the programmer to the test gates which are strictly usable. If this sequential search fails, the following value of the parameters DE and BC is tried and the operations are repeated until all the possible mutual-aid routes between G and G have been exhausted.

If the test for a mutual-aid route between the two selection units G and G fails completely, the operations may be repeated with another mutual-aid unit G having direct links with the imposed unit N and so on until all the possibilities have been exhausted.

It will be seen that the sequential test of the gates of the image network is methodical, is limited strictly to the tests of the links which are capable of providing a route if they are available, and exhaustive, so that it can be said that the route selection is well carried out, both for the direct routes and for those which use the mutualaid, with conditional selection through the whole of the switching network.

THE PRINCIPLE OF THE MARKING AND OF THE CONNECTION OF A SELECTED ROUTE The method of route test on the image network the principle of which has just been explained having led to the selection of a route permitting the junction ABCG to be connected to the subscribers line KLN, either through a direct link DEFG/HJN or through a mutualaid group selection unit G that is to say by borrowing a mutual-aid link DEFGJABC'G' and a secondary selection link DEFG'/ H] N, it remains to effect the marking of said route in the switching network of the automatic switch permitting all its crosspoints to be set in operation and this operation to be checked.

FIGURES 3a, 3b show by way of example, the structure of a connection chain constituting any route through a network in which the crosspoints are formed by means of reed relays having three make contacts and a control coil with two windings, one serving to energise the relay and the other to hold it.

FIGURE 3a relates to a direct route through five switching stages and 3b relates to a mutual-aid route through eight stages.

In these figures, only one crosspoint per switch is illustrated. The connection point, in the switch BC for example, which enables the input link ABC to be connected to the output link BCD has been designated by ABCD.

Five sets of wires appear in FIGURE 3a. They correspond from top to bottom:

to the two line wires of the switching network, transmitting the conversation (wires a and b) to the marking wires (m) enabling the required crosspoints to be energized. These marking wires are rendered unidirectional by means of diodes which are suitably orientated in such a manner as to avoid 1 1 parasitic return paths in the event of marking by coincidence to the holding wire for the route established (Wire to the part of the image network associated with the route illustrated In FIGURES 3a and 3b the marking elements of the image network are represented as electronic gates and its availability elements as break contacts of link holding relays such as v v In a large scale switching network with heavy traffic such as has been taken by way of example, it may be necessary to effect connections at a very high rate, for example of the order of 50 per second; it is therefore essential to provide simultaneity of the operations because in general the crosspoints used have operation times which are too long for it to be possible to consider effecting the connections one by one in the whole of the network.

For this purpose the following simultaneous operations are provided:

(a) Each selection of a direct route causes the engagement of a group selection unit G and a line selection unit N but it may take place simultaneously as many times as there are units G in the exchange, provided that each of them relates to a different unit N.

(b) In order to lead to the connecting through of a selected direct route, the marking of the network only engages the switch BC and the grading sub-unit D through which the route passes in the group selection unit G, and the line selection unit N remains engaged as a whole. This arrangement permits, subject to a suitable inhibition of the engaged fractions, a plurality of markings to be effected in the same unit G for simultaneous connections (up to a maximum corresponding to the number of grading sub-units D) and to execute, in this same unit G, a route selection (direct or with mutual-aid) while these markings are taking place.

(c) When it is necessary to have recourse to mutualaid, which presupposes the intervention of all the group selection units G which are not in the course of effecting a direct route selection (but may be in the course of a plurality of markings for connection), only one search for a mutual-aid route can be carried out at a time in the whole of the network. Nevertheless selection of a direct route can take place simultaneously in the group selection units which are not used for the mutual-aid, as well as marking processes for a connection in any of the group selection units.

Under these conditions it is possible, even if the operating times of the crosspoints are considerable, which is the case with electromechanical systems, to use them in a network of large dimensions while retaining the advantage of conditional selection extended to the whole of the network.

In order that the simultaneous operations provided may be possible, it is necessary for the marking for connection to be confined to the interior of the engaged fractions of the network namely the switches BC, the grading sub-units D and the line selection units N which is achieved by marking the wires (m) at each side of each of the three assemblies asshown in FIGURES 3a, 3b.

More specifically in the case of a direct route to which FIGURE 3a corresponds, marking potentials, which are alternatively positive and negative, are applied at the level of the link ABC, BCD, DEF/HI defining the selected route in the group selection unit G and at the level of the subscribers line KLN. The application of these marking potentials, symbolised in FIGURE 3a by relay' subscribers line KLN. This application is symbolized by contacts m m m m' m' m After every route selection, the logic members associated with the group selection unit G or G are released with the exception of the fractions BC and D in which a marking. should be effected for connection. These fractions of the unit are therefore engaged that is to say they are fictitiously busied with respect to all the markings of the image-network as will be explained later on and they retain the memory of the markings to be applied in accordance with the following rules:

(a) For the marking of the direct route:

, the switch BC retains the memory of its input A to be 'marked (marking m the grading sub-unit DG retains the memory of its input BCand of its output EF to be" marked (markings mg and m 7 the line selection unit N retains the memory of the subscribers line KL (marking m (b) For the marking of a route with mutual-aid:

These marking memories consist of registers associated with the corresponding fractions and to which there are transferred at the end of the route selection, through the logic elements of the selection units, the values of the parameters to be stored.

When, in the case of a direct route, the various markings are thus applied to the'successive sections of the wire (m) of a selected route by the marking members m to m the various crosspoints ABCD to JKL, are energized simultaneously and each set their three make contacts. The first two ensure the continuity of the line wires a and b from the junction to the subscribers line, and the third establishes the continuity of the wire 0 for holding the crosspoints in the route. When all the crosspoints have operated, a holding current passes through the wire 0 and from then on markings can be suppressed over the wire (m). a

In the case corresponding to FIGURE 3b of a route with mutual-aid, the wire c consists of two sections, one of which 0 is identical to that in FIGURE 3a and extends over the selection units G and N, the other 0 extends over the origin selection unit G. Because the holding potential of the first section is supplied by the member v' for detecting the busying of the link DEF/ A'B'C, it follows that the holding current in the first section 0 is only established after the current in the second section 0 v The checking of the connection is effected by determining the presence of a holding current on the wire 0 at the level of the subscribers line KLN (busy detection rnember=v When this has been confirmed, it is possible to remove the inhibition of the members engaged by the marking: switches BC and B'C, sub-units DG and DG, line selection unit N. From then on these members again become available for other route selections.

The object of the division of the wire 0 into two sections at the level of the mutual-aid link by the member v is to prevent the total impedance of the members connected to the wire 0 from being different in the case of a 13 direct route and in the case of a mutual-aid route and thus leading to a difference in the value of the holding current.

In every case the interruption of a route established is effected by interrupting the holding current of the wire at the level of the junction. This interruption is illustrated symbolically in FIGURE 3a by a break contact 1 of a clearing relay in the junction at the level of the link ABC.

The detection of the busy state of the link is effected by verifying the passage of the current through the wire 0 in said link.

In FIGURES 2 and 3a, 3b it is assumed that this current detection is effected by a member: v v v (v' v' v' v v wired onto the wire c and illustrated diagrammatically by a relay having a break contact.

The break contacts of these members appear in the image network illustrated in FIGURE 2. It should be understood that the busy detection member may consist of any system having input terminals connected to the wire 0, output terminals connected to the image network with a suitable decoupling between the inputs and the outputs and such that, when a current passes through the wire c to which the input terminals are connected, the output terminals connected to the image circuit appear in the latter as equivalent to a non-conducting circuit or a closed gate. Conversely if no current is passing through the wire c at the level of the input terminals, that is to say if the link is engaged, the output terminals are equivalent, in the image circuit, to a conducting circuit or an open gate.

LOGIC ELEMENTS FOR CONTROLLING THE CON- NECTION CIRCUIT The logic elements enabling the operation provided above to be carried out are described with reference to FIGURES 4a, 4b which relate respectively to the line selection units N and to the group selection units G and which should be arranged side by side, FIGURE 4a to the right of FIGURE 4b.

FIG. 4a illustrates diagrammatically a line selection unit N, the logic 100 which is associated therewith, an outgoing indicator 200 which is connected on the one hand to the logic 100 through an access device 150 and on the other hand to an access device 250 of a group selection unit G and a store for pending calls 300 which likewise serves as an incoming indicator in the logic 100 and with which there is associated an access device to the stores 350. An incoming indicator associated with an intermediate store for storing the number of a calling subscriber to enable the programmer of a line selection unit N to transfer this number to a computer is described in US. Patent 3,274,343 already mentioned and is illustrated in FIGURE 6 thereof.

The line selection unit N, to which a single subscribers line 10 is illustrated as being connected through its line equipment 11, comprises a switching network 1 and the associated image network 2 constituted as indicated in FIGURES l, 2 and 3a, 3b, a marking circuit of the image network 2 and a line test and marking circuit 3. The marking network 21 of the image circuit which is symbolized in FIGURE 3a by the AND-gate associated with the switch KN stores the parameter K and permits the restriction of the network to the particular value of K as indicated diagrammatically in FIGURE 2 by the contact K. The line test and marking circuit 3 corresponds to the test member and to the marking device respectively designated by v and m in FIGURES 3a, 3b.

The logic section 100 comprises a subscribers register 101 with which there is associated a decoder 102, receiving members 103 and transmitting members 104 for the subscribers address KL and a programmer 105. According to the address KL of a subscribers line 10 recorded in the subscribers register 101, the decoder 102 directs the test and marking circuit 3 so that this tests the state 14 of busying of this line and marks it to permit its connection. The programmer is capable on the one hand of detecting a calling subscriber and of transmitting his number to a computer, and on the other hand of receiving the number of a called subscriber and of controlling the test of the state of occupation of this subscriber and furthermore of effecting the marking of the image network according to the number of the subscriber and of preparing the connection. A programmer capable of fulfilling these functions is described in US. Patent 3,206,553 already mentioned and illustrated in FIGURE 4a thereof.

The logic 100 is in communication with the outgoing indicator 200 and the store for pending calls 300 by means of the access device 150.

The outgoing indicator 200 comprises essentially a programmer 201, a distributor 202 permitting one of the group selection units G to be designated, a decoder 203 permitting one of the line selection units N to be designated, and a group of sets of gates 204 which are in communication on the one hand with all the access devices of the line selection units N, and on the other hand with all the access devices 250 of the group selection units G and which permit the transfer of signals between those of these elements which are designated by the distributor 202 and by the decoder 203, under the action of the programmer 201.

Thus the outgoing indicator 200 is capable of recognizing the call from a group selection unit G of designating the desired line selection unit N and of establishing a temporary connection to this element with the object of finding out its state of availability and possibly of transmitting to it certain information such as a reservation signal and the number of a subscriber to be tested or to be connected.

An outgoing indicator capable of fulfilling these functions is described in US. Patent 3,274,343 already mentioned and is illustrated in FIGURE 6 thereof.

FIGURE 4b illustrates diagrammatically a group selection unit G, the logic 400 which is associated therewith and an access device 450' which ensures the bilateral connection between two computers 600, 600 and the logics such as 400 of the various group selection units G.

The group selection unit G comprises a switching network 5 consisting as shown in FIGURE 1 of ten group sub-units B each of ten switches BC and ten grading subunits D each comprising ten switches CD in stage 4 and ten switches DB in stage 3. Associated with the ten group sub-units B is an assembly 8 of one hundred stores such as 81 individually associated with each of the switches BC. Associated with the ten grading sub-units D is an assembly 9 of twenty stores such as 91 and 92.

The marking store 81 associated with the switch BC records the input parameter A of said switch. The marking stores 91 and 92 associated with the grading sub-unit D record respectively the input parameters B, C and the output parameters E, F of this sub-unit.

The purpose of these marking stores is to energize the corresponding connection marking devices which appear diagramatically at m m or m' m or m' in FIGURES 3a 3b; m is energized according to the contents of 81, m or m' according to the contents of 91, m or m';; according to the contents of 92.

The group selection unit G also comprises the corresponding image network 6 and its associated marking circuit 61 which designates the parameters B, C and D, in question. The image network 6 is illustrated in FIGURE 2. The restriction of this network to the particular values of the selected parameters is symbolised in this figure by the contacts B or B, C or C and D. The contacts B and C belong to the group selection unit G used for the mutual-aid.

When the marking circuits 61 and 21 are in position, the image circuits 6 and 2 respectively apply the marking potential to a plurality of wires q and of wires f leading I a 15 to the test gates 4 which are designated URE 2. I a

The logic 400 associated with the group selection unit G comprises essentially a programmer 401, a route selection register 410, a, current connection .store 420, two transfer circuits 431, 432 controlled by the programmer 401 and a decoder 433. The route selection register is composed of four registers 411-414 respectively associated with the parameters ABC, DEF, KL and N. Associated with the register 412 having the parameters DEF is a advance circuit 415 depending 'on the programmer 401 and the decoder 433. This enables individual test pulses to be" applied in sequence tothe testgates 4 restricted to those which correspond to the direct links leading to the line selection unit N which is required in such ,a ,manner that those of these gates which allow the pulse to pass at their common output terminal 41 characterize the routes which canbe used between; the, extreme points. marked, for example the subscribers line and the junc-- tion ABCG. Associated with the current connection store 420 is a read-out circuit 421, a write-in circuit 422 and an address circuit 423.

The various logic portions 400 and the various. stores for pending calls 300 are respectively connected to the computers 600 and 600' through the two access devices 350 and 450 which are of the type described in US. Patent 3,365,548 issued Jan. 23, 1968.

The programmer 401 is connected through an access device 550550' to a mutual-aid selector the purpose of which is to co-ordinate the test manoeuvres of the mutualaid routes in the various group selection units.

FIGURE 4c illustrates the mutual-aid selector 500 between two group selection units G and G.

In order to make this figure more clear, the access device 550-550' has been divided into two parts respectively connecting the mutual-aid route selector 500, the first 550 to the logic 400 of an origin group selection unit G and the selection 550' to the logic 400' of a group selection unit used for the mutual-aid G. Since each group selection unit may be considered as desired either as an origin unit G or as a mutual-aid unit G the access device 550550 illustrated in FIGURE 4b comprises all the connections illustrated separately at 550 and 550' in FIG- URE 4c.

The mutual-aid route selector 500 comprises essentially a programmer 501, a register 510 the purpose of which is to store the request for mutual-aid while recording in particular the number G of the group selection unit initiating the mutual-aid and the number N of the required line selection unit respectively in sub-registers 511, 512 and a counter-register 520 associated with a decoder 521 enabling it to designate as required and generally sequentially the various group selection units. At every moment, a single output of the decoder 521 is marked, the outputs 5216 and 5216' for example designate the group selection units G and G to the programmers 401 and 401 to which they are respectively connected.

In order to simplify the description of the operation of such an assembly, no distinction will be made between pre-selection, that is to say the connection of a calling subscriber to a junction the purpose of which is to collect the dialling and the final selection, that is to say the connection of a calling subscriber or called subscriber to any kind of junction, local, outgoing or incoming junction, because from the moment when a computer has received the number of the calling subscriber, these two operations, which consist in connecting a subscriber KLN to a junction ABCG in accordance with the diagram in FIGURE 1 are not distinguishable from one another.

The conditions under which the identity of the caller is supplied to the computer are briefly indicated below.

At ordinary times, the programmer 105 of the logic 100 of a line selection unit N ensures the sequential exploration of the line equipment unit 11 by causing the by (DEF) a FIG- .i- 11),. E16, .7 subscribersaddress- KL contained in .thesstore 101- to progress by means of the control wire 106'.

Thesdecoder- -1022Jdistributes pulses to the test circuits 3-untila calling condition is-foundon a line 10. In this q thewir'es 152 using-the code transmitter 104 controlled ber ABC'in the unit G'."-

case, the progra-mmer stopsthe register 101-at the ad'- dress of the-calling subscriberand, throughthe'connection 151', calls-the pending call stores, and the transmission of the identity of the caller KLN'takesplacethrough by the-wire'1-07'. a

"When'thestore 300for pending calls has the complete identity of .the' callerK-LN, it proceeds. to call,- through the access device 350,40! the calculators 600, 60050ne-of thesettakes the 'call and-releases the store"300.

The problem of-selectinga route arises in very casefrom the moment when a computer 600 forexamplejde cidestorconnect a-given subscribe'rs line 10', having the nu'mberKL in "the unitN, to a junction'havin'g the-num In order to be: more lgener al,-the case will be-considered where the subscriber-is called-because it is then necessary; toefiect the: engagement of the-line selection unit N,:an operation which can be dispensed with in the case where the subscriber is calling because his call has already caused the engagement of his selection unit and the latter already has his identity.

OPERATION IN THE CASE OF THE SELECTION OF A DIRECT ROUTE Preliminary operations before a direct route test When the computer 600 decides to connect the junction ABCG to the line KLN, it examines whether the logic 400 of the group selection unit G on which the junction depends is in a position to note the request for a connection and, if so, it connects itself thereto by means of the access device 450.

Through the wire 451, the programmer 401 receives an instruction which invites it to prepare the address circuit 423 and write-in circuit 422 of its store 420 to receive the information transmitted by the computer. If the programmer 401 has indicated that it was ready to note the request, this is because it had already verified the existence of an available store area in the store 420.

The information, transmitted by the computer 600 and written in an area of the store 420 comprise the particular values of the parameters ABC and KLN, but the storage area also comprises locations or pigeon-holes necessary to note the values which will subsequently be attributed to the parameters DEF as well as phase data characterising the state of advance of the connection.

The store 420 comprises as many storage word locations as there may be connections in progress simultaneously in the group selection unit, for example about twenty. The programmer 401 takes an interest in each of them in succession and because of the phase data which accompanies them, it affords them the appropriate treatment before passing to the next one. The majority of phases only require a very short treatment (in general: to check if an expected event has taken place, in which case the phase indication carried in the word is modified); only the route selection phase consists of a series of complex operations, which, once they have been started for one of the pending connections, continue until the end. Thus, in each group selection unit 400, there can never be more than a single connection in progress at a time which is in the said phase; in other words, it is only possible to have at the most one route test process simultaneously per group selection unit.

The information fed into a word location of the store 420 is periodically extracted by the programmer 401 which examines the phase information (connection 424). The first phase relates to the call for the outgoing indicator 200, via lead 212, to make the availability test of the line selection unit N and to reserve it for the selection in question.

Through the connection 434, the programmer assures the transfer, through the circuits 431, of the information read. This transfer goes from the reading circuits 421 to the selection register and relates in particular to the parameters KL and N which are respectively recorded in the sub-registers 413 and 414.

Through the gate 251 of the access device 250 call is recognized by the programmer 201 when its distributor 202 is directed towards the selection element 400 the gate 251 is open through wire 252. At this moment the programmer 201 initiates the availability test for the element N required, by the following means:

the address N contained in 414 is transmitted via gate 253 to the inputs of the decoder of N 203,

the individual output 211 designating the unit N unblocks the gates of the access device 150,

the line selection unit availability signal supplied by the programmer 105 over the wire 111 is then retransmitted to the programmer 401 via 204-254 while the reservation signal is transmitted from 401 to 105 via wire 212, gate 251 and transfer circuit 204, this of course in the case where the line selection unit can be seized,

if the reservation is effective, the connection through the indicator 200 is temporarily maintained in order to permit the transfer of the subscribers address K, L, from the store 413 and the register 101 passing through the set of gates 255, the six wires 213, the set of gates 204, 153 and the code receiver 103 appropriately actuated by the programmer 105 through the wire 109.

When this information transfer process is finished the line selection element is engaged and it has the identity of the subscriber in question. Its programmer immediately effects the availability test of the designated line equipment 11 and it can supply the information regarding availability or busy state of the called subscriber to the programmer 401. This latter requests it by means of an interrogation signal transmitted over the wire 212 and in reply it receives the response (available or busy) over the wire 111.

The connection through the outgoing indicator 200 is then broken and each of the two programmers 401 and 105 resumes its autonomous cycle.

The programmer 105 initiates the marking process of the image network through the circuit 21 (marking effected according to the value of the parameter K and represented symbolically in FIGURE 2 by the closing of the corresponding contact K) and at the same time the marking of the lines KL equipment 11 (marking represented by the contact m in FIGURES 3a, 3b).

The programmer 401 in turn resumes the sequential examination of the various words of the store 420 and each time that it again reads the word concerned in the connection in question it finds there the phase indication: awaiting the end of marking in the line selection unit. Actually the carrying out of this marking instruction may take a certain amount of time, if it is carried out by electromechanical relays and obviously the route test cannot begin until the image network 2 is in position.

In order to find out if the marking has been carried out, the programmer 401 proceeds in precisely the same manner as for testing the availability of the line selection unit that is to say it proceeds to call towards the outgoing indicator 200 and after connection through 200', it transmits an interrogation signal over the Wire 212 and in return it receives a reply over the wire 111.

Selection of a direct route When the programmer 401 receives the marking response signal, it passes to the route selection phase for the corresponding connection inprogress. Until this selection is terminated, it takes no further interest in another word of the store 420.

At the beginning of the phase, through the circuit 431,

the programmer 401 has caused the transfer of all the known information, relating to said connection, to the route selection register 410, namely the parameters A, B, C, K, L and N. The test for a direct route consists of the following sequence of operations directed by the programmer 401:

(a) Display in the register 412 of the initial values of the parameters E and F which are respectively equal to J and H in accordance with the law for the connection of direct links between the various group selection units and the various line selection units.

b) Bringing into position of the marking circuit for the image network 61 in accordance with the values of B, C and D transferred through the connections 416, (D=initial value).

(c) Application in sequence of test pulses to the gates 4 by the outputs of the decoder 433 controlled through the wire 435 by the register 412 assuming successively, under the action of the advance circuit 415, the ten possible values which designate the direct links DEF towards the line selection unit N, (E and F fixed, D varying from 0 to 9).

It has already been indicated that a direct link which can.be used corresponds to a test gate 4 receiving simultaneously a marking at its two inputs q and 7 through the image networks 6 and 2 and consequentiy unblocked by the test pulse applied through 433 to its third input.

Therefore if the programmer 401 receives a pulse over its test wire 41, it knows that a direct route has been found and that the present contents of the register 410 define all its fundamental parameters. All that remains is to initiate the connection of this route, a problem which will be discussed subsequently.

On the other hand, if none of the ten tests is positive, the logic 400 of the group selection unit G should have recourse to the mutual-aid, a process described below.

OPERATION IN THE CASE OF THE SELECTION OF A MUTUAL-AID ROUTE Preparation for the mutual-aid When the programmer 401 having failed to find any direct link decides to have recourse to mutual-aid, it proceeds to call the mutual-aid route selector 500 (FIG- URE 40), by applying a signal to the connection 551.

At normal times, the programmer 501 of the mutualaid route selector 500 distributes pulses in sequence to the various group selection units through the output wires such as 521G-521G of the decoder 521 of which the address resister 520 progresses regularly. These sequential pulses effect a kind of multiplexing in time of the group selection units 400 for the mutual-aid operations. At the same time they permit a sequential analysis of the mutualaid calls through the unblocking of the gates such as 552.

When the register 520 contains the address of an element 400 calling for mutual-aid, the call signal reaches the programmer 501 through the connection 553 and the programmer begins the mutual-aid procedure.

With the register 520 stopped, the decoder 521 marks the wire 5216 and the gates 552-554 of the access device 550 are open. Apart from its call signal over 551, the programmer 401 sends over the connections 555 the value of the parameter N (required line selection unit) extracted from 414 through the connections 417, the transfer circuit 431 and the connections 436.

The programmer 501 records the mutual-aid call in its register 510 by opening the gates 513 and 514 through the connection 515. This causes the transfer of the parameter N, coming from the programmer 401, to the part 512 of the register and the transfer of the number G of the calling group selection unit 400 from the register 520 to the part 511 of the register 510. By means of the decoder G 530 the set of gates 556, 557 relating to the group selection unit initiating the mutual-aid is unblocked in the access device 550 thus establishing the temporary connection between this unit and the mutual-aid selection unit 500. Thereafter, the contents of the register 520 will vary and will designate the mutual-aid units G, while the contents of 511 will remain the same and will continue to designate the initiating unit G. This arrangement enables the mutual-aid route selector 500 simultaneously to connect itself to an unit G and an unit G which are' associated for the mutual-aid, this latter being initiallyindeterminate.

When the programmer 501 has received a call for mutual-aid and has noted it, it effects the reservation of all the group selection units G liable to participate in this mutual-aid, that is to say those having at least one line available in their store 420 and not being in the course of already executing a route selection phase. All the units G which fulfill these conditions mark the associated gate 561 and the reservation signal applied by the programmer 501 to the wire 502 causes the engagement of these units G in the mutual-aid phase through the connection 562. There programmer 401' assumes the position .of being able to receive the necessary information for the mutual-aid selection, namely the values of the parameters N (required line selection unit) and G (initiating group selection unit) contained in the register 510.

The programmer 501 effects the transfer of these parameters by unblocking the gates 517 and 518 through the wire 516. Thus all the programmers 401 engaged receive the parameter G through the connections 567 and the parameter N through the connections 568.

By means of wired translation circuits, these programmers deduced therefrom, in accordance with the rules adopted, the values of the parameters C corresponding vto G and the initial values of the parameters E and ,F

in accordance with the value of J, H. The parameters thus translated are introduced by the programmer 401 into a line which is available in their store for connections in progress 420 with a particular value of the phase .information indicating that it is a question of a mutual-aid and from there to their route selection register 410.

On the basis of this information, the marking circuits of the image networks 6 are brought into position in each mutual-aid unit 400 as in the case of direct selection. Nevertheless, if the parameters D'EF behave in identical manner, the marking corresponding to the parameters B'C is peculiar in so far as initially all the possible values of the parameter B and half of the values of C are simultaneously displayed which, in FIGURE 2, would correspond symbolically to the closing of all the contacts marked B and of half the contacts marked C.

These markings of the image networks have the eifect of causing marking potentials to appear over a plurality of wires q leaving the various units 400. It will be recalled that the marking of the image network 2 of the unit N had the efiect of marking a plurality of wires f leaving said unit N and going towards the various group selection units. Certain of the test gates 4 corresponding to direct selection links (used in secondary selection) are therefore unblocked by the coexistence of the markings at their inputs q and 1''.

Selection of a secondary route The mutual-aid route selector SIE 500 will now control the search for a direct link between one of the units G which is engaged and the line selection until N required.

This search consists in distributing in sequence test pulses to the gates 4 in the various mutual-aid units G in such a manner as to explore all of them one by one, the search being strictly limited to the ten gates corresponding in each of the units G to the links going towards the required unit N.

For this purpose, the programmer 501 causes its register 520 to progress and designate successively the outputs 521 G of the decoder 521. During this time it transmits synchronisation pulses through the wire 503 on the one hand via 557 through the connection 558 towards the unit G (400) initiating the mutual-aid and on the other hand via 563' through the connection 564 towards the unit G (400) designated at this moment by the address contained in 520.

Under the action of the synchronisation pulses on the Wire 564' the programmer 401 applies in sequence test pulses to its ten gates 4 previously defined exactly as in the case of direct selection. If a test is positive a pulse appears over the test wire 41 of the unit 400 and is retransmitted through the programmer 401 of this unit to the connection 565.

On receiving such a pulse through 565 the programmer 501 recognizes that a direct link exists between G and N, and it therefore stops this secondary selection and initiates the selection of a mutual-aid link between the initiating unit G and the mutual-aid unit G.

In the event of all the possibilities examined being exhausted without any test pulses having been received over the wire 565 no mutual-aid route is available and all that would remain would be to indicate to the programmer 401 then to the computer 600 that the connection network was completely blocked.

Selection of a mutual-aid link between G and G For this selection the elementary test operations are coordinated in the programmers 401 and 401 by means of synchronisation pulses applied to the connections 558 and 564. The parameters the value of which must be fixed by this selection are on the one hand B and D which are equal and on the other hand C and E which are likewise equal, modulo 5.

The programmer 501 prepares the mutual-aid selection by opening the gate 519 through the connection 504. It follows that the parameter G (number of the mutualaid unit contained in the register 520) is transmitted via 519, 556 and the connection 559 to the programmer 401. By means of a wired translation circuit, this programmer deduces from the parameter G, in accordance with the rules adopted, the value of the parameter P which it should use, and it introduces it into its register 410.

The selection of a mutual-aid link betewen G and G, the object of which is to fix the values of B (or D) and of C (or E), comprises the following sequence of operations controlled by the programmer 501 which delivers synchronisation pulses over the wire 503 and observes the test wires 560 connected to the wire 41 through the programmer 401 and 565 connected to the test wire 41' through the programmer 401.

(a) While the decoder 433' of the unit 400 continues to designate the same test gate which supplied a positive reply during the secondary selection when all the possible values of the parameters B and C were displayed, the programmer 401 causes the contents of the part B'C of the register 411 to progress and at each of the fifty possible values, causes the sending of a test pulse by means of the control lead 435 to this gate 4 which will be designated for example by 4 In synchronism, the programmer 401 causes the contents of the part DE of its register 412 to progress, so that the parameters B and D remain constantly equal in the two registers 410 and 410 as do the parameters C and E (modulo 5).

Referring to FIGURE 2, it will be assumed that the upper portion, designated in the figure by 6 and 2, represents diagrammatically the image network of the secondary selection between the mutual-aid unit G and the line selection unit N (for this all the designation included in the zone 6 of the figure should be regarded as having primes and the portion 6 should be ignored). It will further be assumed that the left-hand portion 6 and the lower portion 6 in FIGURE 2 represent diagrammatically (with the appropriate prime marks) the image networks of the mutual-aid selection between the units G and G.

Viewed thus, the upper gate (DEF) in FIGURE 2 is the gate designated above as 4 In the course of the progress of the register B'C' (411) the image network 6 of the group selection unit G is modified because while the contact D remains unchanged, the ten contacts B are closed successively as are the five contacts C which can be used in the imagenetwork 6.

It follows that it is only for some of the possible values of the parameters BC' in general that the gate 4 will continue to be conducting.

When the programmer 501 sees the test pulse reappear over the wire 565, it stops the progress in the parameters B'C' (and DE) and passes to the following operation (b).

(b) Now it is the programmer 401 of the initiating group selection unit which, at the instigation of the programmer 501 and without the values of the parameters B, CD, and E, being modified will apply a test pulse to the gate of the mutual-aid link which corresponds to these values of the parameters D and E and to the imposed value of F in accordance with the number of the unit G which is designated at this moment by the .programmer 501 of the mutual-aid route selector. If this mutual-aid link is free, this test pulse will pass through the gate which, actually, as the lower portion of. FIG- URE 2 shows, receives a marking at its input q through the contacts which correspond to the parameters D', B and C, and a second marking at its input f through the contacts representing the parameters B and C selected in the unit G.

When the programmer 501 sees a test pulse appear over the wire 560 which extends the test wire 41, it deduces from that that the selection of the mutual-aid is terminated and it indicates to the programmer 401 and 401' that they should begin the connection of the route in accordance with the parameters which they have in their registers 410 and 410'. At the same time it signals to the other programmers 401' which have been engaged with the mutual-aid that they may be released and then it releases itself.

If the above sequence of operations b is fruitless, there is a return to the previous sequence a to try a fresh possible value of BC and of DE. When all the values of BC have been tried without success there is a return to the previous sequence of secondary route selection by seeking to obtain a reply through a new test gate 4, which may lead to trying other selection units G (400) by progression of the address contained in the register 520 until all the possibilities have been exhausted.

CONNECTION OF THE ROUTES SELECTED Marking 0 the route to be connected When the route selection is terminated, each programmer 401 engaged in the selection comprises in its route selection register 410 all the parameters which it needs to actuate the marking circuit and to cause the operation of the connection points.

The programmer 401 transfers the parameter A to the marking store 81 associated with the switch designated by the parameters B, C. It transfers the parameters B, C and the parameters E, F to the marking stores 91 and 92 respectively of the grading sub-unit designated by the parameter D.

The corresponding information leaves the portions 411 and 412 of the register 410, and is directed in accordance with the values of B, C by the connections 437 and, in accordance with the value of D, by the connections 438, 439. This direction is effected by the transfer circuit 432 actuated by the wire 441.

Having thus been filled, the marking stores decode the information received and apply the marking for connection to the appropriate links of the network 5. The store 81 actuates the marking point noted m in FIGURES 3a, 3b, store 91 actuates the point m (or m' and the store 92 actuates m (or m' It is known that the marking point m associated with the line equipment 11 has been previously actuated by the marking circuit 3.

The switches BC and the grading sub-units D the marking stores of which are full, are marked as unavailable for the selection of routes so long as they have not been liberated after verification of the connection. This result is obtained by an inhibition, in the marking circuit 61, of the marking relating to the busy values of the parameters D and BC. This inhibition (not illustrated in the figures) has the effect, for example of preventing the closure of a contact such as D in FIGURE 2 if the value of the parameter D comprised by the marking circuit 61 is a forbidden value.

Checking the connection After this transfer to the marking stores and their consecutive engagement, the programmer 401 rewrites the line in its store 420 relating to the connection which it has just initiated, supplementing it in accordance with the information contained in its register 410 and adding a piece of phase information awaiting checking of the connection.

The programmer 401 then resumes its sequential examination of the words in the store for the connections in progress 420. It therefore returns periodically to read the line relating to the connection in question.

Finding that said connection in progress is at the awaiting checking phase, which it recognizes by the outputs 424 of the read-out circuit 421, it calls the outgoing indicator 200 with the object of being connected to the programmer of the line selection unit N the address of which is included in the word of store 420.

By means of a process already encountered several times, the programmer 401 transmits over the wire 212 an interrogation signal to which the programmer 105 will reply over the wire 111 by an end-of-operation signal if it has been found, using its line test circuit 3, that the test point v (FIGURE 3) relating to the subscriber KL is active, that is to say that all the connection points in the route have set their holding contact (continuity of the wire 0).

In this case, the programmer 401 releases the marking stores 81, 91, 92 used by the connection (which causes the withdrawal of the markings on the wire m) and, in turn, the programmer 105 releases its marking stores 101 and 21 and then again becomes available after having checked that all the members of the logic portion of the line selection element N have returned to rest.

In conclusion, the programmer 401 calls the computer 600 through the access device and when it is connected thereto it transfers the end-of-operation information thereto. It can likewise transmit to it all the parameters of the route through the connections 452. After which it erases the word of the store 420 relating to the connection which has been effected.

We claim:

1. A switching arrangement for an automatic telecommunication exchange comprising:

(a) a switching network including subscribers lines,

- a plurality of line selection units, a plurality of group selection units, direct links connecting said line selection units to said group selection units, and junction circuits, each line selection unit including first and second access terminals, a plurality of line selection switches, line selection partial links connecting said line selection switches therebetween, said first access terminals of the line selection units being connected to said subscribers lines and said second access terminals of the line selection units being connected to said direct links, each of said group selection units including first and second access terminals, a plurality of group selection switches, group selection partial links connecting said group selection switches therebetween, certain first access terminals of the group selection units being connected 23 to said junction circuits and certain second access terminals of the group selection units being connected to said direct links, and mutual aid links connecting the other first access terminals of given group selection units to the other second access terminals of different group selection units;

(b) a routing network having the same pattern as the switching network, including partial, direct and mutual-aid routing links respectively associated with the partial, direct and mutual-aid switching links of the switching network, common nodes between links respectively associated with the line selection and group selection switches, routing links connected to the same switch, gating means inserted in said routing links, and means for actuating said gating means in response to the availability and busy conditions of the partial, direct and mutual-aid switching links associated to the routing links in which they are inserted;

(c) means for cyclically selecting complete routing links originating at a subscribers line and terminating at a junction circuit and formed by serially connected partial, direct and mutual-aid routing links when the gating means inserted therein are open; and

(d) means for marking and connecting the partial, di-

rect and mutual-aid switching links respectively associated to the partial, direct and mutual routing links forming the complete routing link selected.

2. A switching network for an automatic telecommunication exchange as set forth in claim 1, in which the means for cyclically selecting complete routing links originating at a subscribers line and terminating at a junction circuit comprises first choice selecting means for cyclically selecting direct complete routing links formed by serially connected partial and direct routing links through a line selection unit and a group selection unit, the gating means inserted therein being open, means for signaling the condition that no such direct complete routing link has been selected and second choice selecting means initiated in response to said signaling means for cyclically selecting mutual-aid complete routing links formed by serially connected partial links in a line selection unit and a first and a second group selection units, mutual-aid link between said first and second group selection units and direct link between said second group selection unit and line selection unit, the gating means of said mutual-aid complete routing link being open.

3. A switching network for an automatic telecommunication exchange as set forth in claim 1, in which the partial, direct and mutual-aid switching links are four wire links comprising two speech wires, a control wire for controlling the crosspoints of the switches of the line selection and group selection units and a hold wire for holding said crosspoints and the gating means inserted in the routing links and the means for actuating said gating means in response to the availability and busy conditions of the switching links are respectively contacts of relays inserted in the routing links and the windings of said relays inserted in the hold wires of the switching links.

4. A switching arrangement for an automatic telecommunication exchange comprising:

(a) a switching network including subscribers lines,

a plurality of line selection units, a plurality of group selection units, direct links connecting said line selection units to said group selection units, and junction circuits, each line selection unit including first and second access terminals, a plurality of line selection switches, line selection partial links connecting said line selection switches therebetween, said first access terminals of the line selection units being connected to said subscribers lines and said second access terminals of the line selection units being connected to said direct links, each of said group selection units including first and second access terminals, a plurality of group selection switches, group selection partial links connecting said group selection switches therebetween, certain first access terminals of the group selection units being connected to said junction circuits and certain second access terminals of the group selection units being connected to said direct links, and mutual-aid links connecting the other first access terminals of given group selection units to the other second access terminals of dilferent group selection units;

(b) a routing network having the same pattern as the switching network, including partial, direct and mutual-aid routing links respectively associated with the partial, direct and mutual-aid switching links of the switching network, common nodes between links respectively associated with the line selection and group selection switches, routing links connected to the same node corresponding to switching links connected to the same switch, each direct routing link being divided into a first direct routing half-link on the side of the line selection units and a second direct routing half-link on the side of the group selection units, gating means inserted in said routing links, gates each connected to a first and a second direct routing half-links and means for actuating said gating means in response to the availability and busy conditions of the partial, direct and mutual-aid switching links associated to the routing links in which they are inserted;

(c) means for cyclically testing the gates connected to first and second direct routing half-links which are parts of complete routing links originating at a subscribers line and terminating at a junction circuit and formed by serially connected partial and mutual-aid routing links and two direct routing halflinks of which th gating means inserted therein are open; and

(d) means for marking and connecting the partial,

mutual-aid and direct switching links respectively associated to the partial, mutual routing links and first and second direct routing half-links forming the complete routing link the gates of which are passing.

5. A switching arrangement for an automatic telecommunication exchange comprising:

(a) a switching network including subscribers; lines, a plurality of line selection units, a plurality of group selection units, direct links connecting said line selection units to said group selection units, and junction circuits, each line selection unit including first and second access terminals, a plurality of line selection switches, line selection partial links connecting said line selection switches therebetween, said first access terminals of the line selection units being connected to said subscribers lines and said second access terminals of the line selection units being connected to said direct links, each of said group selection units including first and second access terminals, a plurality of group selection switches, group selection partial links connecting said group selection switches therebetween, certain first access terminals of the group selection units being connected to said junction circuits and certain second access terminals of the group selection units being connected to said direct links, and mutual-aid links connecting the other first access terminals of given group selection units to the other second access terminals of ditferent group selection units;

(b) a routing network having the same pattern as the switching network, including partial, direct and mutual-aid routing links respectively associateed with the partial, direct and mutual-aid switching links of the switching network, common nodes between links respectively associated with the line selection and group selection switches, routing links connected to the same node corresponding to switching links connected to the same switch, each direct routing link being divided into a first direct routing half-link on 26 terminating at a junction circuit and formed by a partial routing link through a first group selection unit, a mutual-aid routing link, a partial routing link through a second group selection unit, a direct routing link and a partial routing link through a line the side of the line selection units and a second direct 5 selection unit, these links being serially connected routing half-link on the side of the group selection and the gating means inserted therein being Open;

units, gating means inserted in said routing links gates and each connected to a first and a second direct routing (e) means for marking and connecting the partial, di-

half-links, and means for actuating said gating means 10 rect and mutual-aid switching links respectively asin response to the availability and busy conditions of sociated to the partial direct and mutual routing the partial, direct and mutual-aid switching links aslinks forming the complete routing link selected by sociated to the routing links in which they are said first choice selecting means and the composite inserted; complete routing link selected by said second choice (c) first choice means for cyclically selecting com- 15 selecting means.

plete routing links origination at a subscribers line and terminating at a junction circuit and formed by References Cited serially gonnected partial and direct routing links of UNITED STATES PATENTS which t e gating means inserted therein are open and means for signaling the occupation of all said 20 2227488 V1941 Colhs et a1 complete routing links; 3,211,836 10/1965 Warman 179-18.21

. 3 272 924 9/1966 Warman 179-1821 (d) second choice means controlled by said signallng means for cyclically selecting composite complete routing links originating at a subscribers line and WILLIAM C. COOPER, Primary Examiner. 

